Starting in the 1930s, designers began using elements of aircraft aerodynamics to smooth out the boxy-looking automobile. Some designs that were ahead of their time when exhibited during the early 1930s included "teardrop" streamlining of the car's rear; a configuration similar to what would become known as 'fastback' 25 years later." 'Fastback' was first recognized as a definition by Merriam-Webster in 1954, many years before the term 'hatchback' was popularized and entered the dictionary in 1970. Opinions vary as to whether the terms are mutually exclusive.
A contributor to an automotive-interest website singles out the unusual Stout Scarab from the early 1930s as "[p]ossibly the epitome of the early fastback definition". The Packard 1106 Twelve Aero Sport Coupe, introduced in 1933, is cited elsewhere as a fastback that foreshadowed trends which continued into the 1940s.
Starting in 1935, Australian automakers introduced fastback body design that became known as the "Sloper". It was first designed by General Motor's Holden as one of the available bodies on Oldsmobile, Chevrolet, and Pontiac chassis. The Sloper design was added by Richards Body Builders in Australia to Dodge and Plymouth models in 1937, by Ford Australia in 1939 and 1940, as well as a sloper style made on Nash chassis. According to automotive historian G.N. Georgano, "the Slopers were advanced cars for their day."
Numerous fastbacks were also made in America, where the style was previously called "torpedo back". They included Cadillac's Series 61 and 62 Club Coupes as well as various models from General Motors, Ford, and Chrysler. In 1948, the all new Hudsons were available a fastback body for the Brougham and sedan models.
Fastbacks provide an advantage in developing aerodynamic vehicles with a low drag coefficient. The Kamm tail is a related concept. The trend towards a more steeply raked rear window on traditional three-boxsedans blurs the distinction between fastback and notchback designs. However, the roof of a true fastback design slopes down continuously to the rear, most often to the base of the trunk at the rear bumper. There is no distinct change of angle to a rear deck, whereas most four-door cars with steeply raked rear windows have less angled trunk lids; also high tails to maximize cargo space.
In 2008, the fastback design appeared on a concept car that almost defies categorization, the Chrysler ecoVoyager, that "Jack Telnack, former design chief for the Ford Motor Company, declared, 'It’s a fastback van.'" New types of crossover vehicles and different body proportions made possible by technological advances and new powerplants, are changing the shape of automobiles. Traditional nomenclature describing distinct vehicle bodies, such as the three-box sedan (engine compartment, passenger cabin and trunk) will vanish.
When the rear window of a car with a fastback profile is integral to a lid or 'fifth door' (i.e. a hatch) giving access to the trunk area, the car may also fit the classification of hatchback or liftback. The late-model Toyota Celica and the Chevrolet Vega are examples.
A definition of a fastback by Road & Track addresses this distinction: "A closed body style, usually a coupe but sometimes a sedan, with a roof sloped gradually in an unbroken line from the windshield to the rear edge of the car. A fastback naturally lends itself to a hatchback configuration and many have it, but not all hatchbacks are fastbacks and vice versa."